Neuro - Auditory System Flashcards
What are the 3 parts of the ear?
Outer
Middle
Inner
Where is the ear organ located?
In the petrous part of the temporal bone - the hardest bone in the body
What makes up the outer ear
The pinna and the ear canal
What are the functions of the outer ear
Capture sound and focus it on the tympanic membrane
Amplify some frequencies by resonance in the canal
Protect the ear from external threats
How does the outer ear protect from external threats
Hairs in the canal
Wax provides physical barrier and also pH of wax kills things coming into the ear
What is the function of the middle ear
Amplification of sound
What makes up the middle ear
Tympanic membrane
3 ossicles with their associated muscles, tendons and ligaments
How does the middle ear amplify sound
Focuses vibrations from large surface area onto the smaller oval window to increase pressure
Uses leverage from the incus-stapes joint to increase the force on the oval window
What makes up the inner ear
Cochlea
What is the function of the inner ear
transduce vibrations into nervous impulses and also provide a frequency and intensity analysis of sound
What are the 3 cochlea compartments
Scala vestibuli
Scala media
Scala tympani
What is perilymph
Fluid found in the scala vestibuli and tympani which is high in sodium
What is endolymph
Fluid found in the scala media high in potassium
Where is the organ of Corti located
In the basilar membrane of the scala media
How is the Basilar membrane organised
Tonotopically - there s a narrow and tight base with a wide and loose apex
What frequencies cause vibrations in the base of the Basilar membrane
High frequency
What frequencies cause vibrations in the apex of the basilar membrane
Low frequency
What makes up the organ of Corti
Thousands of hair cells (both IHC and OHC)
What is the tectorial membrane
Located above the hair cells and allow deflection of hair cells to cause cell depolarisation
What cells are in constant contact with the organ of Corti
OHC
What nerves do IHC mainly carry
95% afferent fibres of the auditory nerve
What nerves do OHC mainly carry
95% efferent fibres of the auditory nerve
What is the function of afferent auditory nerves
Transduction of sound into nerve impulses
What is the function of efferent auditory nerves
Modulation of the sensitivity of the response (active amplifying of the OHC)
What are the hairs of hair cells called
Stereocilia
What does stereocilia deflection lead to
Deflection towards the longest cilium causes the opening of K channels and thus depolarisation
Explain the process of transduction
Vibrations cause the IHC to contact the tectorial membrane and thus their stereo cilia deflect and K channels are opened. There is influx of K into the cell and thus depolarisation, leading to the opening of voltage gated calcium channels.
These channels open and therefore calcium causes the exocytosis of glutamate out of the fair cells and thus a nervous response in propagated through the afferents of the auditory nerve
Describe the pathway of auditory information from the cochlea to the cerebral hemisphere
Spiral ganglions from the cochlea extend to the cochlear nucleus.
Auditory information then reaches the superior olive and crosses contralaterally (some fibres stay ipsilateral).
Fibres then travel to the inferior colliculus in the brainstem and then to the medial geniculate body in the thalamus. Finally fibres reach the auditory cortex in the cerebral hemisphere.
What is the need for tonotopic arrangement of hearing
If we can’t discriminate different frequencies then we cannot discriminate or interpret speech
What is frequency
Cycles per second, perceived tone
Pitch
What is amplitude
Sound pressure, subjective attribute correlated with physical strength (loudness)
What is the range of frequency for hearing
20-20,000 Hz
What is active amplifying
OHC can contract or elongate to alter whether or not IHC will come into contact with the tectorial membrane - this means that we can hear sounds that are too soft and our ears aren’t damaged from sounds that are too loud
What is the normal range of amplitude
0-120dB
What type of scale is the decibel scale
Log scale
What is the need for a log scale for decibels
Allows us to compress the scale on a graph - reflects the fact that many physiological processes are non linear
How does hearing alter with age
Hearing acuity decreases with age, particularly higher frequencies - medium and low can be affected with the progression of a hearing loss
What are the 3 questions in a hearing assessment?
Is there hearing loss?§
If so - of what degree?
Of what type?
What procedures can we use to test hearing
Tuning fork Audiometry Central processing assessment Tympanometry Otoacoustic emission Electrocohcleography Evoked potentials
What is a tuning fork used for
Establish probable presence or absence of a hearing loss with a significant conductive component, therefore provide early and general information if audiometry is not available
What is a Weber test
Vibrate fork to see if patent hears on both sides the same
What is a Rinne test
Directly stimulate the bone as endolymph vibrates to see if there is a problem with the middle/ inner ear
What is pure tone audiometry (PTA)
Science of measuring hearing acuity for variations in sound intensity and frequency
What does an audiometer do
The device used to produce sound of varying intensity and frequency
What is an audiogram
Where the hearing thresholds are listed to define if there is a hearing loss or not
What is a normal hearing threshold for an audiogram
0-20dB
What is central processing assessment
Assessment of hearing abilities rather than just tone detection
What are examples of central processing assessment
Sound localisation
Filtered speech
Speech in noise
What is tympanometry
Examination used to test the condition of the middle ear and mobility of the tympanic membrane and the conduction bones by creating variations of air pressure in the ear canal
What is A in tympanometry
Normal
What is C in tympanometry
Negative middle ear pressure
What can be the causes of B in tympanometry
Middle ear effusion
Perforation of the tympanic membrane
Eustachian (pharyngotympanic) tube dysfunction
Occluded ear canal
What are otoacoustic emissions
Sounds produces by the normal cochlea, by the OHC as they expand and contract
When are OAEs performed
Newborn hearing screening and hearing loss monitoring
What is an auditory brainstem response
Electrical responses from the auditory pathway evoked by clicks (auditory evoked potential)
When are ABRs used
More commonly used in clinic and doesn’t require attention from the patient - alterations in latency of waves can point to the location of a deficit.
Commonly used in babies and children
What affects cortical potentials
Cortical potentials could be affected in neurological conditions or processing problems
What is conductive hearing loss
Problem is located in the outer or middle ear
What is sensorineural hearing loss
Problem is located in the inner ear or the auditory nerve
What is mixed hearing loss
Conduction and transduction of sound are affected therefore the problem stems from multiple parts of the ear
What do we see in an audiogram for conductive hearing loss
Bone conduction normal but air conduction shows hearing loss
What do we see in an audiogram for sensorineural hearing loss
bone and air conduction are both affected equally
What do we see in an audiogram for mixed hearing loss
Bone and air conduction are both affected but not equally
What are the classifications of hearing loss
Mild, moderate, severe, profound
What are causes of outer ear hearing loss
Wax
Foreign body
What are causes of middle ear hearing loss
Otitis
Otosclerosis
What are causes of inner ear hearing loss
Presbycusis
Ototoxicity
What are causes of nerve hearing loss
VIII nerve tumour
What are the 4 domains of hearing loss treatment
Underlying cause
Hearing aid
Cochlear implant
Brainstem implant
What are hearing aids
Hearing aids amplify sound but do not replace any structure
What do we need to have a hearing aid
Functioning hair cells
What is a cochlear implant
Replaces the function of hair cells by receiving sound analysing it, transforming it into electrical signals and sending an electric impulse directly to the auditory nerve
What do we need to have a cochlear implant
Functional auditory nerve
What is a brainstem implant
When the auditory nerve is affected, electrical signal can be sent to a set of electrodes places directly into the brainstem
When is a brainstem implant advised
People with bilateral important auditory nerve damage - is a risky procedure
